One answer is...
Seeing how people drive ground-based vehicles (50,000 deaths from
auto accidents in the USA alone each year), do you really want them
flying around in multiton vehicles full of flammable fuel, too?!
A less frightening but still sad answer is that even modern jetpacks only
work for about 30 seconds or so. So you might look really cool and
futuristic in one, but you wouldn't get very far.
About that book:
http://www.paleofuture.com/blog/2007/5/16/wheres-my-jetpack-2007.html
http://www.paleofuture.com/blog/2008/1/23/bell-aviations-rocket-pack-1964.html